Memory device and memory system with sensor

ABSTRACT

According to one embodiment, a memory device includes a first address memory storing a first address; a controller which is based on a first interface which transmits a signal serially and outputs a first command in accordance with the first interface; and a memory which stores data in a nonvolatile manner, is based on the first interface, and stores received write data in an address based on the first address when the memory receives the first command.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional application of U.S. patent application Ser. No.14/460,021, filed Aug. 14, 2014, which is a Continuation-in-partapplication of U.S. patent application Ser. No. 14/198,398, filed Mar.5, 2014, which claims the benefit of U.S. Provisional Application No.61/869,293, filed Aug. 23, 2013, the entire contents all of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory device and amemory system with a sensor.

BACKGROUND

An MRAM (Magnetic Random Access Memory) is known as a nonvolatilesemiconductor memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a memory system according to a firstembodiment;

FIG. 2 is a block diagram of an MRAM;

FIG. 3 is a circuit diagram of one memory cell;

FIG. 4 is a block diagram of an address memory and address memorycontroller;

FIG. 5 is a diagram showing one example of a Gray code;

FIG. 6 is a timing chart showing signals supplied to a memory device;

FIG. 7 is a block diagram of an address memory and an address memorycontroller according to a second embodiment;

FIG. 8 is a block diagram of an address memory and address memorycontroller according to a third embodiment;

FIG. 9 is a diagram showing the relationship between an input and outputof an MSB extractor obtained when an address is formed of four bits;

FIG. 10 is a block diagram of an address memory and address memorycontroller according to a fourth embodiment;

FIG. 11 is a waveform diagram of write clock CLK and clock CLKR;

FIG. 12 is a diagram showing the relationship between an input andoutput of an MSB extractor obtained when an address is formed of fourbits;

FIG. 13 is a circuit diagram showing one example of the MSB extractor;

FIG. 14 is a circuit diagram showing another example of the MSBextractor;

FIG. 15 is a block diagram of an address memory and address memorycontroller according to a modification;

FIG. 16 is a block diagram of an address memory and address memorycontroller according to a fifth embodiment;

FIG. 17 is a block diagram of another example of the memory systemaccording to the first embodiment;

FIG. 18 is a block diagram of a memory system according to a sixthembodiment;

FIG. 19 is a block diagram of a nonvolatile memory according to thesixth embodiment;

FIG. 20 illustrates an example of a flow of a signal on signal line SIin accordance with a serial transmission interface;

FIG. 21 illustrates signals transmitted and received between a modulecontroller and the nonvolatile memory in the sixth embodiment;

FIG. 22 is a block diagram of a memory system according to a seventhembodiment;

FIG. 23 illustrates signals transmitted and received between a modulecontroller and an address memory controller in the seventh embodiment;

FIG. 24 illustrates a second example of signals transmitted and receivedbetween a module controller and an address memory controller in theseventh embodiment;

FIG. 25 is a block diagram of a memory system according to an eighthembodiment;

FIG. 26 illustrates signals transmitted and received between a modulecontroller and a second address memory controller in the eighthembodiment;

FIG. 27 illustrates signals transmitted and received between a modulecontroller and an address memory controller in a second example of theeighth embodiment;

FIG. 28 illustrates signals transmitted and received between a modulecontroller and a second address memory controller in a ninth embodiment;

FIG. 29 illustrates signals transmitted and received between a modulecontroller and the second address memory controller in a second exampleof the ninth embodiment;

FIG. 30 illustrates an example of a parity generation matrix accordingto a tenth embodiment;

FIG. 31 illustrates an example of an operation to generate parityaccording to the tenth embodiment

FIG. 32 illustrates an example of a decryption matrix according to thetenth embodiment

FIG. 33 illustrates an operation for error correction with thedecryption matrix of FIG. 32;

FIG. 34 is a block diagram of a nonvolatile memory according to thetenth embodiment;

FIG. 35 illustrates a second example of a parity generation matrixaccording to the tenth embodiment;

FIG. 36 illustrates a third example of a parity generation matrixaccording to the tenth embodiment;

FIG. 37 illustrates a fourth example of a parity generation matrixaccording to the tenth embodiment;

FIG. 38 illustrates a fifth example of a parity generation matrixaccording to the tenth embodiment; and

FIG. 39 illustrates a sixth example of a parity generation matrixaccording to the tenth embodiment.

DETAILED DESCRIPTION

According to one embodiment, a memory device comprises a first addressmemory storing a first address; a controller which is based on a firstinterface which transmits a signal serially and outputs a first commandin accordance with the first interface; and a memory which stores datain a nonvolatile manner, is based on the first interface, and storesreceived write data in an address based on the first address when thememory receives the first command.

With the recent development of computer networks and miniaturization ofcommunication devices and measurement units, a system such as machine tomachine (M2M) in which information items are mutually exchanged betweenmultiple devices without human operations to automatically optimize theoperation control, is proposed. In such a system, information items ofvarious devices are transferred via the network. One example of thedevice is a sensor device, in which information items such astemperatures, vibrations, brightness, acceleration or angles aremeasured by means of various sensors and the measurement data aretransmitted to the network. The operation power supply of the sensordevice is obtained by use of a battery or energy harvester, except for acase wherein a stable power supply voltage is applied. Therefore,lowering the power consumption of components contained in the sensordevice becomes more important in the field of M2M and sensor devicenetworks. A memory used for storing measurement data is also one of thecomponents of the device and, in the embodiments, it is assumed that anonvolatile memory is used, the technique related to lowering the powerconsumption is addressed.

In a nonvolatile memory having a mode in which the write process issuccessively performed to store the measurement results of the sensor,it is necessary to interrupt supply of power to the nonvolatile memoryto reduce a consumed current after completion of the write process. Inthis case, the nonvolatile memory itself should record an internaladdress used to continue the write process after the power supply isturned on next time. The object of this embodiment is to suppress thepower consumption of the nonvolatile memory by reducing the number ofto-be-rewritten bits of the nonvolatile memory as far as possible. Inorder to realize this, in the embodiments, the internal address isformed by a Gray code and a circuit for controlling the internal addressused for starting the write process to be rewritten only to a valueobtained by increasing the previously stored address by a power of twois provided. As a result, the number of to-be-rewritten bits in thenonvolatile memory for address recording is 20 bits at maximum in theconventional technique since, for example, an address identifying aspace of one megabit is expressed by 1M=1048576=2 to the power oftwenty, but the number of to-be-rewritten bits is suppressed to two bitsat maximum by applying the technique of the embodiments. As a result,the power consumption of the nonvolatile memory can be suppressed.

Embodiments of this invention are now described with reference to theaccompanying drawings. In the following explanation, components havingthe same functions and configurations are denoted by the same symbolsand a repetitive explanation is made only when required. The entiredescription for a particular embodiment is also applicable to anotherembodiment unless it is explicitly mentioned otherwise or obviouslydenied.

First Embodiment 1. Whole Configuration

FIG. 1 is a block diagram of a memory system 10 according to a firstembodiment. The memory system 10 includes a power supply circuit 11,module controller 12, sensor 13 and memory device 14. The memory device14 includes an address memory 15, address memory controller 16 andnonvolatile memory 17.

The sensor 13 makes measurements and transmits measurement data as writedata to the nonvolatile memory 17. The write data are in a digital form.In contrast, the measurement data generated by the sensor 13 may be inan analog format. In such a case, analogue measurement data areconverted into digital write data by an analog to digital (AD)converter. Although not illustrated by FIG. 1, an AD converter islocated between the output of the sensor 13 and the nonvolatile memory17. A write address used for storing measurement data in the nonvolatilememory is generated by means of the address memory 15 and address memorycontroller 16.

The module controller 12 controls the whole operation of the memorysystem 10. The module controller 12 transmits measurement control signalMSC to the sensor 13 to control the measurement operation of the sensor13 by use of measurement control signal MSC. The module controller 12transmits a write clock CLK and an enable signal ENA to the addressmemory controller 16. Further, the module controller 12 transmits thewrite clock CLK and memory control signal MEC to the nonvolatile memory17 to control the operation of the nonvolatile memory 17 (for example,write operation) by use of the memory control signal MEC.

The module controller 12 may include a sequencer, for example. Thesequencer is responsible for, among the functions of the modulecontroller 12, functions in accordance with predefined procedures.

For example, the sequencer generates the measurement control signal MSC,the enable signal ENA and the memory control signal MEC. Moreover, thesequencer may also include a function for managing a schedule.Specifically, in one embodiment of operation, the sequencer is activatedperiodically based on, for example, a timer or when a particular eventoccurs. When activated, the sequencer in turn activates the sensor 13and the memory device 14 through the start of the power supply from thepower supply circuit 11, and executes measurement and storing of data.Alternatively, in another embodiment of operation, the sequencer mayactivate the memory device 14 to store data when the measurement dataexhibits a sign of a change. Some of the functions of the sequencer maybe implemented by a microcomputer.

The power supply circuit 11 generates and supplies various power supplyvoltages to the module controller 12, sensor 13 and memory device 14. Asthe power supply circuit 11, for example, a battery, solar battery orenergy harvest could be used. The memory system 10 may be configured tobe supplied with external power supply voltages.

The address memory 15 is configured by use of a nonvolatile memory andstores address information in a nonvolatile fashion. Address informationstored by means of the address memory 15 is the initial addressgenerated when the previous write access is made to the nonvolatilememory 17. The address memory controller 16 reads address information(initial value) from the address memory 15. Then, the address memorycontroller 16 generates a write address by use of the addressinformation and transmits the write address to the nonvolatile memory17. Write access is made to the nonvolatile memory 17 by use of thewrite address. The address memory 15 may be implemented by some of thefunctions of the nonvolatile memory 17.

For example, the memory system 10 could be configured by use of onesemiconductor chip. Alternatively, the memory system 10 may beconfigured by a plurality of modules, each module being configured by asemiconductor chip and connected on a system board. Further, the memorysystem 10 may be configured as a multi-chip module in one package.Alternatively, the nonvolatile memory 17, address memory 15 and addressmemory controller 16 could be designed and manufactured as onesemiconductor chip. In FIG. 1, a method for reading data stored in thenonvolatile memory 17 and outputting the data to the exterior of thememory system 10 is not clearly described, but a circuit having such afunction can be additionally provided.

FIG. 17 is a block diagram of another example of the memory system 10according to the first embodiment. FIG. 17 also illustrates an ADconverter 18, which is omitted in FIG. 1. The AD converter 18 receivesthe analogue measurement data from the sensor 13, and outputs thedigital measurement data as the write data. The memory system 10 furtherincludes an output circuit 19. In accordance with an instruction OCCfrom the module controller 12, the output circuit 19 receives data fromthe nonvolatile memory 17, and outputs the received data to outside thememory system 10. The data output to outside the memory system 10 isexecuted wirelessly, for example. For that purpose, the output circuit19 includes a wireless communication module. The wireless communicationmodule follows instructions by the module controller 12 to add thereceived data to a radio signal to transmit it outside the memory system10. The module controller 12 follows instructions from, for example,outside, to read data in the nonvolatile memory 17 in order to output itoutside the memory system 10. Alternatively, the module controller 12starts the output of data in the nonvolatile memory 17 to outside thememory system 10 at a particular timing.

The measurement by the sensor 13 and writes to the nonvolatile memory 17of measurement data (or, write data) may be executed at a low frequency.In such a case, parallel execution of measurement, data writes and datatransmissions by the output circuit 19 at a low frequency may beinefficient, and therefore may consume much power. To address this, themodule controller 12 executes low-frequency measurements and data writeswithout outputting such to the outside in succession while remaining ON,and collects data up to a particular quantity before transmitting it enbloc outside the memory system 10 using the output circuit 19, forexample.

The memory system 10 may be used for an application in which it observesand measures small-size data items one after another, and stores them,for example. For example, the memory system 10 may be normally poweredOFF, and be used in an application in which it is turned on sporadicallyto store relatively-small-size data items one after another at a lowfrequency, and outputs accumulated data outside at a particular timing.

2. Configuration of Nonvolatile Memory 17

Next, a configuration example of the nonvolatile memory 17 is described.As the nonvolatile memory 17, various types of semiconductor memoriessuch as an MRAM (Magnetic Random Access Memory), ReRAM (ResistanceRandom Access Memory), PCRAM (Phase-Change Random Access Memory) andflash memory (for example, NAND flash memory) can be used. In thepresent embodiment, one example in which an MRAM is used as thenonvolatile memory 17 is described.

FIG. 2 is a block diagram of the MRAM 17. The MRAM 17 includes a memorycell array 20, row decoder 21, column controller 22, input/outputcircuit 23 and controller 24.

The memory cell array 20 is configured by use of memory cells MCarranged in a matrix form. In the memory cell array 20, bit line pairsBL, /BL and word lines WL are arranged.

FIG. 3 is a circuit diagram of one memory cell MC. Memory cell MCincludes a magnetoresistive effect element (MTJ (Magnetic TunnelJunction) element) 25 and select transistor 26. As the select transistor26, for example, an n-channel MOSFET is used. One end of the MTJ element25 is connected to a bit line BL and the other end thereof is connectedto the drain of the select transistor 26. The gate of the selecttransistor 26 is connected to a word line WL and the source thereof isconnected to a bit line /BL.

The row decoder 21 is connected to the word lines WL. The row decoder 21selects one of the word lines WL based on a row address.

The column controller 22 is connected to the bit line pairs BL, /BL. Inthe data write mode, the column controller 22 selects one of the bitline pairs based on a column address and passes a write current througha selected memory cell via the selected bit line pair to write data inthe selected memory cell. Further, in the data read mode, the columncontroller 22 selects one of the bit line pairs based on a columnaddress to read data from the selected bit line pair. In order toperform the above operation, the column controller 22 is configured toinclude a column decoder, a column selector, sense amplifiers, a writedriver and the like.

The input/output circuit 23 transmits write data input from the exteriorto the column controller 22 and outputs read data input from the columncontroller 22 as output data to the exterior.

The controller 24 performs overall control of the various operations ofthe MRAM 17. For example, the controller 24 receives an address, writeclock CLK and memory control signal MEC from the exterior and controlsthe write operation and read operation based on the above signals.

3. Configuration of Address Memory 15 and Address Memory Controller 16

The configuration of the address memory 15 and address memory controller16 is now described in more detail. FIG. 4 is a block diagram of theaddress memory 15 and address memory controller 16. The address memorycontroller 16 corresponds to the components other than the addressmemory 15 among the components of FIG. 4. That is, the address memorycontroller 16 includes a register 30, Gray code counter 31, roundingcircuit 32 and bit comparator 33.

In the present embodiment, address information stored in the addressmemory 15 is described with a Gray code. FIG. 5 is a diagram showing oneexample of a Gray code. The Gray codes are codes in which the number ofbits that vary between adjacent codes is always one. In FIG. 5, therelationship between binary codes, decimal codes and Gray codes isshown.

The register 30 temporarily stores address information read from theaddress memory 15. The Gray code counter 31 counts up addressinformation (Gray code) stored in the register 30 each time write clockCLK is input.

The rounding circuit 32 rounds the final output of the Gray code counter31 to set the number of bits to be rewritten in the address informationread from the address memory 15 to two bits at maximum. Specifically,the rounding circuit 32 outputs a value that is equal to or larger thanthe final output of the Gray counter 31 and larger than the output ofthe register 30 (initial value of the Gray code counter 31) by one or apower of two, for example, 2, 4, 8, . . . .

The bit comparator 33 compares the output of the rounding circuit 32with the output of the register 30 for each bit. Then, the bitcomparator 33 transmits only bits that are inconsistent with theoriginal value to the address memory 15.

4. Operation

The operation of the memory system 10 with configuration described aboveis now described. FIG. 6 is a timing chart showing signals supplied tothe memory device 14.

When the power supply of the memory system 10 is turned on, the modulecontroller 12 asserts the enable signal ENA. Then, the module controller12 generates the write clock CLK which is in response to write accessesand transmits write data from the sensor 13 to the nonvolatile memory 17in synchronism with the write clock CLK.

Further, the address memory controller 16 supplies a write address tothe nonvolatile memory 17 in synchronism with write clock CLK.Specifically, when the enable signal ENA is asserted, the address memorycontroller 16 reads address information from the address memory 15 andcounts up the write address each time the write clock CLK is input wherethe address information is used as an initial value. The nonvolatilememory 17 stores write data in the memory cell of the write address.

When a series of write accesses is completed, the module controller 12negates the enable signal ENA. Once the enable signal ENA is negated,the address memory controller 16 writes address information in theaddress memory 15. The address information written in the address memory15 here is the final address used in the series of write accesses andwill be read, and becomes an initial value when the enable signal ENA isnext asserted. After this, the module controller 12 interrupts supply ofthe power from the power supply circuit 11.

In the present embodiment, the enable signal ENA is supplied from theexterior of the memory device 14. However, the memory device 14 mayinclude a circuit that detects the level of the power supply, forexample, and the memory device 14 may be configured to assert the enablesignal ENA when the power supply voltage becomes equal to or higher thana preset first potential and negate the enable signal ENA when the powersupply voltage becomes equal to or lower than a preset second potential.For stable operation of the circuit, it is desirable to set the secondpotential lower than the first potential.

Next, a more detailed operation of the address memory controller 16 isdescribed with reference to FIG. 4. When the enable signal ENA isasserted, the address information is read from the address memory 15 andis temporarily stored in the register 30. The address information storedin the register 30 is used as an initial value of the Gray code counter31.

The module controller 12 activates the write clock CLK upon each writeaccess to the nonvolatile memory 17. The Gray code counter 31 counts upthe address from the initial value according to the Gray code rule foreach pulse of the write clock CLK. For a write access to the nonvolatilememory 17, an output of the Gray code counter 31 is used as a writeaddress. That is, write accesses are made to the nonvolatile memory 17sequentially from an address next to the address stored in the addressmemory 15 after the memory system 10 is started. There are several knowncircuits as the Gray code counter 31 of the present embodiment andtherefore a detailed description thereof is omitted here.

When a series of write accesses is completed, the enable signal ENA isnegated and the rounding circuit 32 outputs a value that is the equal toor larger than the final output of the Gray code counter 31 and largerthan the output of the register 30 (initial value of Gray code counter31) by one or a power of two, for example, 2, 4, 8, . . . .

The bit comparator 33 compares the output of the rounding circuit 32with the output of the register 30 for each bit. Only bits that areinconsistent as the result of comparison by the comparator 33 arewritten in the address memory 15. Bits that are consistent are notwritten and the original values (read data) are maintained. Due to thecharacteristic of the Gray code, the number of to-be-rewritten bits istwo at maximum when the address is changed by a power of two.

5. Effect

As a comparison example, if address information stored in the addressmemory 15 is not formed of a Gray code but formed of a binary code and abinary counter is used instead of the Gray code counter 31, for example,it is necessary to rewrite four bits when a 4-bit address is changed byone from “0111” to “1000”. For example, since an address is 20 bits in amemory being accessed by use of addresses of 1 megabit, there is apossibility that 20 bits may be rewritten at maximum.

On the other hand, in the present embodiment, when address informationstored in the address memory 15 is rewritten after a series of writeaccesses (all of the write accesses from the time when the enable signalENA is asserted until the signal is negated) is completed, the number ofto-be-rewritten bits is suppressed to two at maximum. As a result, thepower consumption required for rewriting address information stored inthe address memory 15 can be greatly reduced.

Further, write access is made to the nonvolatile memory 17 by use of awrite address formed of a Gray code that is the output of the Gray codecounter 31. Therefore, since a change in an address for each writeaccess can be suppressed to one bit, the number of address lines whichare charged and discharged can be reduced and, as a result, the powerconsumption can be reduced.

Data is not written in a storage region corresponding to an addressskipped by rounding circuit 32 in the storage region of the nonvolatilememory 17. For example, the unwritten region may be managed by writingan invalid flag in the unwritten region.

Second Embodiment

A second embodiment is an embodiment in which a counter that counts upan address is configured by a binary counter, which can be easilyrealized. FIG. 7 is a block diagram of an address memory 15 and addressmemory controller 16 according to the second embodiment. The addressmemory controller 16 includes a register 30, rounding circuit 32, bitcomparator 33, Gray-to-bin converter 34, binary counter 35 andbin-to-Gray converters 36, 37.

The Gray-to-bin converter 34 converts address information formed of aGray code to a binary code. The binary counter 35 counts up addressinformation converted to a binary code by the Gray-to-bin converter 34each time the write clock CLK is input. The bin-to-Gray converters 36,37 each convert address information formed of a binary code to a Graycode.

In order to convert a Gray code to a binary, the exclusive OR (XOR) of abit and all of the more significant bits than that bit is calculated.For example, the following operations are performed to convert a 4-bitGray code address G3, G2, G1, G0 to binary B3, B2, B1, B0.

B3=G3

B2=G3 XOR G2

B1=G3 XOR G2 XOR G1

B0=G3 XOR G2 XOR G1 XOR G0

In order to convert a binary to a Gray code, the exclusive OR of a bitand a bit that is one-bit more significant than that bit is calculated.For example, the following operations are performed to convert 4-bitbinary

B3, B2, B1, B0 to a Gray code address G3, G2, G1, G0.

G3=B3

G2=B3 XOR B2

G1=B2 XOR B1

G0=B1 XOR B0

The exclusive OR operation is known in the art and therefore a detailedexplanation thereof is omitted here.

The operation of the address memory controller 16 with the aboveconfiguration is now described. Address information stored in theregister 30 is supplied to the Gray-to-bin converter 34. The Gray-to-binconverter 34 converts address information formed of a Gray code to abinary according to the table of FIG. 5. Address information convertedto a binary by the Gray-to-bin converter 34 is used as an initial valueof the binary counter 35.

The module controller 12 activates the write clock CLK each time writeaccess is made to the nonvolatile memory 17. The binary counter 35counts up the address from the initial value for each pulse of the writeclock CLK.

The bin-to-Gray converter 36 converts a count of the binary counter 35to a Gray code according to the table of FIG. 5. For write access to thenonvolatile memory 17, a Gray code converted by the bin-to-Grayconverter 36 is used as a write address.

When a series of write accesses is completed, the enable signal ENA isnegated and the rounding circuit 32 outputs a value that is equal to orlarger than the final output of the binary counter 35 and larger thanthe output of the Gray-to-bin converter 34 (initial value) by one or apower of two, for example, 2, 4, 8, . . . . The bin-to-Gray converter 37converts an output of the rounding circuit 32 formed of a binary to aGray code.

The bit comparator 33 compares the output of the bin-to-Gray converter37 with the output of the register 30 for each bit. Only bits that areinconsistent as the result of comparison by the bit comparator 33 arewritten in the address memory 15. Bits that are consistent are notwritten and the original values (read data) are maintained. Due to thecharacteristic of the Gray code, the number of to-be-rewritten bits istwo at maximum when the address is changed by a power of two. As aresult, the same effect as that of the first embodiment can be obtained.

Further, a binary is converted to a Gray code by the bin-to-Grayconverter 36 and write access is made to the nonvolatile memory 17 byuse of a write address formed of the Gray code. Therefore, since achange in an address for each write access can be suppressed to one bit,the number of address lines which are charged and discharged can bereduced and, as a result, the power consumption can be reduced. Thecount of the binary counter 35 can be used as a write address. That is,the bin-to-Gray converter 36 can be omitted and write access is made tothe nonvolatile memory 17 by use of a write address formed of a binary.

Third Embodiment

A third embodiment shows a concrete configuration example of a roundingcircuit 32. FIG. 8 is a block diagram of an address memory 15 andaddress memory controller 16 according to the third embodiment.

A binary counter 38 whose initial value is “0” is newly provided inparallel with the binary counter 35 that uses a value read from theaddress memory 15 and is supplied via the Gray-to-bin converter 34 as aninitial value. The binary counter 38 counts up an address from aninitial value=0 in response to the write clock CLK generated for eachwrite access. An output of the binary counter 35 is used as a writeaddress.

The rounding circuit 32 includes an MSB (most significant bit) extractor32A and adder 32B. After a series of write accesses is completed (theenable signal ENA is negated), the MSB extractor 32A (1) outputs thefinal output of the binary counter 38 as it is when the final output isone or a power of two and (2) outputs a value that is larger than thefinal output of the binary counter 38 and is a power of two when thefinal output is neither one nor a power of two. More specifically,first, the MSB extractor 32A extracts the MSB of the final output of thebinary counter 38. Then, the MSB extractor 32A outputs the final outputof the binary counter 38 as it is when the final output is 1. Further, abinary that is a power of two has 1 in only one bit and 0 in the otherbits. Therefore, the MSB extractor 32A outputs the final output of thebinary counter 38 as it is when the final output of the binary counter38 has only one bit of 1 and outputs a value that is a power of two inwhich only the more significant bit next to the MSB is 1 when the finaloutput of the binary counter 38 has plural bits of 1.

FIG. 9 is a diagram showing the relationship between an input and outputof the MSB extractor 32A obtained when an address is formed of fourbits. The MSB extractor 32A outputs a value of a power of two as it iswhen the 4-bit address is a power of two and outputs a value obtained byrounding up the value to a power of two in other cases.

The adder 32B adds an output (initial value) of a Gray-to-bin converter34 to an output of the MSB extractor 32A. The output of the adder 32B isinput to a bit comparator 33 via a bin-to-Gray converter 37. Asdescribed before in detail, also, in the third embodiment, the sameeffect as that of the first embodiment can be obtained.

Fourth Embodiment

A fourth embodiment shows another configuration example of the roundingcircuit 32. FIG. 10 is a block diagram of an address memory 15 andaddress memory controller 16 according to the fourth embodiment.

In the fourth embodiment, the number of pulses of clock CLKR input to abinary counter 38 is less by one than the number of pulses of the writeclock CLK generated for each write access. For this control operation,the address memory controller 16 includes a clock reducer (CLK reducer)39. The clock reducer 39 receives the write clock CLK after the enablesignal ENA is asserted and generates the clock CLKR obtained byeliminating the first one pulse of the write clock CLK (shifted by oneclock cycle). FIG. 11 is a waveform diagram of write clock CLK and clockCLKR. The function of the clock reducer 39 can be realized by use of aknown method using a shift register or the like.

The binary counter 38 is supplied with a clock having one pulse reducedfrom that of the third embodiment and the MSB extractor 32A outputs avalue of a power of two in which only one-bit more significant than theMSB of the final output of the binary counter 38 is 1 (the output valueis 1 when the final output of the binary counter 38 is 0). FIG. 12 is adiagram showing the relationship between an input and output of the MSBextractor 32A obtained when an address is formed of four bits.

The function of the MSB extractor 32A can be relatively easily realized.FIG. 13 is a circuit diagram showing one example of the MSB extractor32A. Inputs of the MSB extractor 32A are A3, A2, A1, A0 and outputsthereof are B3, B2, B1, B0. In FIG. 13, the correspondence table betweeninputs A2, A1, A0 and outputs B3, B2, B1, B0 is also shown. Input A3 isfixed at 0.

The MSB extractor 32A includes inverters 41 to 44, AND gates 45 to 47and NOR gate 48. Input A0 is connected to the inputs of the AND gate 47and NOR gate 48. Input A1 is connected to the inputs of the inverter 43,AND gate 46 and NOR gate 48. The output of the inverter 43 is connectedto the input of the AND gate 47. Input A2 is connected to the inputs ofthe inverter 42, AND gate 45 and NOR gate 48. The output of the inverter42 is connected to the input of the AND gate 46. Input A3 is fixed at 0and is connected to the input of the inverter 41. The output of theinverter 41 is connected to the input of the AND gate 45. The output ofthe AND gate 45 is connected to the input of the AND gate 47 via theinverter 44. The output of the NOR gate 48 corresponds to output B0, theoutput of the AND gate 47 corresponds to output B1, the output of theAND gate 46 corresponds to output B2 and the output of the AND gate 45corresponds to output B3.

FIG. 14 is a circuit diagram showing another example of the MSBextractor 32A. The MSB extractor 32A includes inverters 50, 51 and NORgates 52 to 54. Input A0 is connected to the inputs of the inverter 51and NOR gate 54. The output of the inverter 51 is connected to the inputof the NOR gate 53. Input A1 is connected to the inputs of the inverter50 and NOR gates 53, 54. The output of the inverter 50 is connected tothe input of the NOR gate 52. Input A2 is connected to the inputs of theNOR gates 52 to 54. The output of the NOR gate 54 corresponds to outputB0, the output of the NOR gate 53 corresponds to output B1, the outputof the NOR gate 52 corresponds to output B2 and input A2 corresponds tooutput B3.

In the above description, the first pulse of the write clock CLK isneglected and the remaining pulses are output after the enable signalENA is asserted according to the function of the clock reducer 39.However, the essence of the present embodiment lies in that the numberof pulses of clock CLKR input to the binary counter 38 is different fromthe number of pulses of the write clock CLK. For example, the sameeffect can be obtained if the last pulse of the write clock CLK isneglected when the enable signal ENA is negated. Further, the outputclock of the clock reducer 39 may not be necessarily output insynchronism with the write clock CLK.

As described above in detail, according to the fourth embodiment, likethe first embodiment, when address information stored in the addressmemory 15 is rewritten after a series of write accesses is completed,the number of to-be-rewritten bits can be two bits at maximum. As aresult, the same effect as that of the first embodiment can be obtainedin the fourth embodiment.

(Modification)

A write address supplied to the nonvolatile memory 17 can be convertedto a Gray code. FIG. 15 is a block diagram of an address memory 15 andaddress memory controller 16 according to a modification. In FIG. 15, abin-to-Gray converter 60 is added to the circuit of FIG. 10. Thebin-to-Gray converter 60 converts an output of a binary counter 35 to aGray code. As a result, a write address formed of a Gray code issupplied to the nonvolatile memory 17. According to the modification,since a change in an address for each write access can be suppressed toone bit, the number of address lines used for charging and dischargingcan be reduced and, as a result, the power consumption can be reduced.

Fifth Embodiment

In the second to fourth embodiments, the binary counter is used forcounting up the address, but in the fifth embodiment, a Gray codecounter is used for counting up the address and the Gray-to-binconverter and bin-to-Gray converter are omitted.

FIG. 16 is a block diagram of an address memory 15 and address memorycontroller 16 according to the fifth embodiment. The address memorycontroller 16 includes two Gray code counters 31, 61. The Gray codecounter 31 has the same function as that of the first embodiment. TheGray code counter 61 counts up an address based on the clock CLK fromthe clock reducer 39. The output of the Gray code counter 61corresponding to the clock CLKR is as shown in FIG. 5.

A rounding circuit 32 includes an added value extractor 32C and adder32B. The added value extractor 32C receives the final output of the Graycode counter 61. Then, the added value extractor 32C outputs a valuethat is equal to or larger than the final output of the Gray codecounter 61 and is a power of two.

The adder 32B performs a count-up operation once according to the Graycode rule to add a value of a power of two to the initial value whilethe position of the least significant bit is adequately changed.Specifically, the adder 32B performs the following operations.

(1) When the final output of the Gray code counter 61 is 0 (when writeclock CLK is one pulse), the least significant bit of the initial valueis set as the least significant bit and the count-up operation isperformed once to the initial value according to the Gray code rule.That is, the counting up is performed only once according to the Graycode rule.

(2) When the final output of the Gray code counter 61 is 1 (when writeclock CLK is two pulses), the second bit from the least significant bitof the initial value is set as the least significant bit and thecount-up operation is performed once to the initial value according tothe Gray code rule and the least significant bit is inverted.

(3) When the added value is “4 (the second power of 2)”, the third bitfrom the least significant bit is set as the least significant bit, thecount-up operation is performed once to the initial value according tothe Gray code rule, the least significant bit is fixed and the secondbit from the least significant bit is inverted.

(4) When the added value is “8 (the third power of 2)”, the fourth bitfrom the least significant bit is set as the least significant bit, thecount-up operation is performed once to the initial value according tothe Gray code rule, the least significant bit and second bit are fixedand the third bit from the least significant bit is inverted.

A similar idea is applied when the added value is the fourth power ormore of 2.

The operation of the other circuits is the same as that of the firstembodiment.

As described above in detail, in the fifth embodiment, when addressinformation stored in the address memory 15 is rewritten after a seriesof write accesses (all of the write accesses while the enable signal ENAremains asserted) is completed, the number of to-be-rewritten bits canbe suppressed to two at maximum. Further, a memory system 10 can berealized without using the Gray-to-bin converter and bin-to-Grayconverter.

Sixth Embodiment

The sixth embodiment relates to application of a particular interface tothe memory system 10, and is applicable to any of the first to fifthembodiments.

FIG. 18 is a block diagram of a memory system 10 according to the sixthembodiment. The memory system 10 includes the power supply circuit 11,the module controller 12, the sensor 13, and the memory device 14. Thememory system 10 may further include an AD converter 18 and/or an outputcircuit 19. The memory device 14 includes the address memory 15, theaddress memory controller 16, and the nonvolatile memory 17. In thesixth embodiment, the nonvolatile memory 17 is configured to operate inaccordance with an interface which transmits data serially.Specifically, the nonvolatile memory 17 is configured to recognizecommands based on an interface which transmits data serially, andreceive and output data in accordance with such an interface. Theinterface which transmits data serially is referred to as a serialtransmission interface herein. Examples of the serial transmissioninterface include a serial peripheral interface (SPI) andinter-integrated circuit (I²C) interface. The serial transmissioninterface is suitable for small data transmission and can transmit lessdata than in a case of parallel data transmission within the same periodand consumes less power.

FIG. 19 is a block diagram of the nonvolatile memory 17 according to thesixth embodiment. The nonvolatile memory 17 is an MRAM as in the firstembodiment, for example. The MRAM 17 operates in accordance with theserial transmission interface as described above. In accordance withthis, the MRAM 17 includes an input/output circuit 71 instead of theinput/output circuit 23 of the first embodiment. The input/outputcircuit 71 supports the serial transmission interface. Specifically, theinput/output circuit 71 receives a serial signal on a signal line SI,receives a chip (or, memory) enable signal /CS, and receives the clockCLK. The input/output circuit 71 transmits a serial signal to the outputcircuit 19 on a signal line SO.

On the signal line SI, a signal, such as commands, addresses, and data,flows toward the input/output circuit 71. FIG. 20 illustrates an exampleof the flow of the signal on the signal line SI, chip enable signal /CSand clock CLK in accordance with a serial transmission interface. Thenonvolatile memory 17 is enabled while a signal /CS remains asserted.FIG. 20 relates to an example of a write. In the write based on theserial transmission interface, commands, addresses, and data all flow onthe signal line SI. The nonvolatile memory 17 takes in the signal on thesignal line SI in units of bytes (each byte including eight bits) insynchronization with the write clock CLK.

The nonvolatile memory 17 receives a write command, an address, and dataon the signal line SI as illustrated in FIG. 20. The write commandinstructs a data write, and is illustrated as 02h as an example, and hasa size of one byte, for example. The address specifies memory cells MCin which data will be written among the memory cells MC of thenonvolatile memory 17, and is referred to as a write address. The dataare data which will be written, and has a size of one byte, for example.FIG. 20 illustrates a case of a write to the nonvolatile memory 17 witha capacity of 1G bits. In accordance with this, a write addressindicates the write-target address by four bytes.

In such context, six bytes of a signal (a command, an address, and data)need to be transmitted for a write of one-byte data.

On the signal line SO, the signal, such as data, flows out of theinput/output circuit 71. During a read, read data from the memory cellsMC flows on the signal line SO.

Referring back to FIG. 18, the nonvolatile memory 17 operates inaccordance with the serial transmission interface as described above. Inaccordance with this, the module controller 12 is also configured tooperate in accordance with the serial transmission interface, and itoperates in accordance with the same interface as that of thenonvolatile memory 17. Specifically, the module controller 12 isconfigured to generate commands based on the serial transmissioninterface, and receive and output data in accordance such an interface.In accordance with the difference in the interface, the modulecontroller 12 of the sixth embodiment outputs signals different fromthose in the first embodiment. Specifically, the module controller 12outputs a signal /CS, and transmits the memory control signal MEC, suchas a command and an address, to the nonvolatile memory 17 on the signalline SI.

The write data from the sensor 13 are transmitted to the nonvolatilememory 17 on the signal line SI. The address memory 15 can store theaddress information in accordance with the Gray code in accordance withother embodiments, or in any other form. For the case of storing basedon the Gray code, the address memory controller 16 has the featuresdescribed in the first to fifth embodiments. For the case of the addressinformation not being stored in the form based on other embodiments, theaddress memory controller 16 merely increments the value of the addressinformation in the address memory 15 by a particular amount (forexample, 1) to generate a write address.

Referring to FIG. 21, the operation of the memory system 10 will now bedescribed. FIG. 21 illustrates signals transmitted and received betweenthe module controller 12 and the nonvolatile memory 17 in the sixthembodiment.

As in the first embodiment, when the memory system 10 is turned on, themodule controller 12 asserts the signals /CS and ENA. The modulecontroller 12 then generates the write clock CLK, and executesoperations described in the following in synchronization with the writeclock CLK.

As described in the first embodiment, a write address can be generatedby the address memory controller 16 from the address information in theaddress memory 15. For this reason, the module controller 12 does notneed to transmit a write address to the nonvolatile memory 17.Therefore, the module controller 12 writes data in the nonvolatilememory 17 without specifying a write address. The module controller 12transmits a second write command to the nonvolatile memory 17 on thesignal line SI. The second write command (no-address write command) isdifferent from the regular write command accompanied by a write addressof FIG. 20, and is illustrated by a value, for example, F2h, which isdifferent from that for the regular write command for the purpose ofdistinction from the regular write command. The second write commandinstructs for the following signal to be recognized as the write data,and for the write data to be written in a write address receivedseparately.

The module controller 12 controls the sensor 13 to make it transmit thewrite data on the signal line SI following the second write command. Themodule controller 12 does not transmit a write address. The modulecontroller also asserts the signal ENA in parallel with or after thetransmission of the second write command. In response to the assertedsignal ENA, the address memory controller 16 generates a write addressfrom the address information and supplies the generated write address tothe nonvolatile memory 17.

When the nonvolatile memory 17 receives the second write command, itrecognizes the second write command and executes the operationinstructed by the second write command. Specifically, the nonvolatilememory 17 writes the data received after the second write command in thememory cells MC specified by the write address received from the addressmemory controller 16.

For additional data writes, the operation described so far is repeated.Specifically, the module controller 12 maintains the asserted enablesignal /CS and keeps outputting the write clock CLK. While thenonvolatile memory 17 keeps receiving the asserted enable signal /CS andthe write clock CLK, it sequentially writes write data being receivedduring the period. Specifically, the module controller 12 controls thesensor 13 to make it transmit additional write data on the signal lineSI. The nonvolatile memory 17 keeps incrementing the write-targetaddress by a unit amount and consecutively writes the write data itemsbeing received. The module controller 12 does not need to transmit awrite command every time of write of write data.

When a series of writes is completed, the module controller 12 negatesthe enable signal ENA and writes the last address in the current seriesof write accesses as the address information in the address memory 15 asin the first embodiment. The module controller 12 then stops the powersupply by the power supply circuit 11.

As described, in the sixth embodiment, the address information isstored, and the nonvolatile memory 17 and the module controller 12 usethe serial transmission interface and support a write command which doesnot require transmission of a write address. A write address isseparately generated from the address information, and, therefore, doesnot need to be transmitted from the module controller 12. For thisreason, the signal transmitted to the nonvolatile memory 17 from themodule controller 12 for a data write only includes a command and data,and has a size of two bytes in total according to the FIG. 21 example.This quantity is smaller than that of the regular write command (FIG.20). A reduced time of transmission of the signal results in decreasedpower consumption by the memory system 10.

Seventh Embodiment

The seventh embodiment relates to an example of application a particularinterface to the memory system 10, and is applicable to any of the firstto sixth embodiments.

FIG. 22 is a block diagram of the memory system 10 according to theseventh embodiment. In the seventh embodiment, the address memorycontroller 16 is configured to operate in accordance with the serialtransmission interface. Specifically, the address memory controller 16is configured to recognize commands based on the serial transmissioninterface, and receive and output data in accordance with such aninterface. In accordance with the address memory controller 16 using theserial transmission interface, the module controller 12 also operates inaccordance with the same serial transmission interface. Specifically,the module controller 12 outputs the enable signal ENA, and transmits amemory control signal AMC, such as a command and an address, to theaddress memory controller 16 on a signal line SIM. The address memorycontroller 16 is enabled while the enable signal ENA remains asserted.Moreover, the module controller 12 receives an output AMO from theaddress memory controller 16 on a signal line SOM. For a case of theaddress memory 15 being implemented by some of the functions of thenonvolatile memory 17, the signal lines SIM and SOM are identical withthe signal lines SI and SO, respectively.

The nonvolatile memory 17 may or may not be based on the serialtransmission interface. FIG. 22 illustrates an example where thenonvolatile memory 17 is based on the serial transmission interface asin the sixth embodiment.

FIG. 23 illustrates signals transmitted and received between the modulecontroller 12 and the address memory controller 16 in the seventhembodiment. Update of the address information in the address memory 15may be requested. The update request is made from outside the memorysystem 10 to the module controller 12, for example. The update requestis received with the new address information.

When address information update is requested, the module controller 12asserts the enable signal ENA, outputs the write clock CLK, andtransmits an address write command (write address write command) to theaddress memory controller 16 on the signal line SIM. The address writecommand is different from the write command 02h and F2h, is illustratedby FIG. 23 as E2h, and has a size of one byte, for example. The modulecontroller 12 transmits the value of the new address to the addressmemory controller 16 on the signal line SIM after the address writecommand. The address has a size of four bytes, for example.

When the address memory controller 16 receives the address writecommand, it recognizes the address write command and executes theoperation instructed by the address write command. Specifically, theaddress memory controller 16 updates the value in the address memory 15with the value of the address received from the module controller 12.When the update of address information is completed, the modulecontroller 12 negates the enable signal ENA.

The writes are the same as those in other embodiments. Specifically,when a data write occurs, the module controller 12 executes the write inaccordance with the address information last updated by the addresswrite command.

Furthermore, the address information in the address memory 15 may berequested from outside the memory system 10. The request of read ofaddress information is made from outside the memory system 10 to themodule controller 12, for example. In order to deal with such a request,an address read command can be defined. FIG. 24 illustrates the secondexample of signals transmitted and received between the modulecontroller 12 and the address memory controller 16 in the seventhembodiment.

When a read of the address information is requested, the modulecontroller 12 asserts the enable signal ENA, outputs the read clockCLKB, and transmits an address read command (write address read command)to the address memory controller 16 on the signal line SIM. The addressread command is different from the regular read command accompanied by aread address, and is illustrated by FIG. 24 as E3h, and has a size ofone byte, for example. A read address specifies the memory cells MC fromwhich data will be read among the memory cells MC of the nonvolatilememory 17.

When the address memory controller 16 receives the address read command,it recognizes the address read command and executes the operationinstructed by the address read command. Specifically, the address memorycontroller 16 reads the address information in the address memory 15,and transmits the read address information to the module controller 12on the signal line SOM. The module controller 12 outputs the receivedaddress information to outside the memory system 10 through control ofthe output circuit 19 when necessary. FIG. 24 illustrates an examplewhere the address information has a size of four bytes. When the read ofaddress information is completed, the module controller 12 negates theenable signal ENA.

As described, according to the seventh embodiment, the addressinformation can be written from outside the memory system 10 by theaddress write command. Moreover, the address information can be accessedfrom outside the memory system 10 by the address read command.

Eighth Embodiment

The eighth embodiment relates to an example of application of aparticular interface to the memory system 10, and is applicable to anyof the first to seventh embodiments.

FIG. 25 is a block diagram of the memory system 10 according to theeighth embodiment. The module controller 12, the address memorycontroller 16, and the nonvolatile memory 17 operate in accordance withthe serial transmission interface as in the sixth and seven embodiments.

The memory device 14 of the eighth embodiment further includes a secondaddress memory 15 b and a second address memory controller 16 b. Thesecond address control circuit 16 b can have the same components andconnections as the address memory controller 16, and operates inaccordance with the serial transmission interface. The second addressmemory controller 16 b receives a signal ENAB, the write clock CLK, andthe read clock CLKB from the module controller 12 and receives a memorycontrol signal AMCB, such as a command and an address on the signal lineSIMB. Moreover, the second address memory controller 16 b supplies anoutput AMOB to the module controller 12 on a signal line SOMB. For acase of the second address memory 15 b being implemented by some of thefunctions of the nonvolatile memory 17, the signal lines SIMB and SOMBare identical with the signal lines SI and SO, respectively.

The second address memory 15 b can have the same features as the addressmemory 15, and in that case the description for the address memory 15 isapplicable.

Data in the nonvolatile memory 17 may be read to outside the nonvolatilememory 17 at a particular timing. A read is executed for output tooutside the memory system 10, for example, as described in the firstembodiment. For example, the module controller 12 starts a read of datafrom the nonvolatile memory 17 based on an instruction from outside thememory system 10 or a predetermined timing (for example, based on atimer).

Similarly to writes, consecutive reads may be executed from more thanone area with consecutive addresses of the nonvolatile memory 17. Insuch a case, when the address of the area from which the data was readlast is specified, the address which follows or is based on thespecified address is used as the start position, and a read address doesnot need to be specified separately. The serial transmission interfaceof the eighth embodiment or other embodiments supports consecutive readsfrom areas with consecutive addresses of the nonvolatile memory 17 witha specification reduced from the regular read accompanied by readaddresses. For example, when the nonvolatile memory 17 which supportssuch a serial transmission interface receives the read clock CLKB whileit keeps receiving the asserted enable signal /CS, it keeps incrementingthe address from the start position by a unit amount and reads dataconsecutively from the resultant addresses. The I²C, for example,supports such a read.

For such a read, if the read address of the start position is specified,read addresses do not have to be individually specified. Based on this,the read address from which the data was read last is stored in thesecond address memory 15 b as in the write. The second address memory 15b can store the address information in accordance with the Gray code inaccordance with other embodiments or in any other form.

The module controller 12 supplies the read clock CLKB to the nonvolatilememory 17 and the second address memory 15 b. Moreover, the modulecontroller 12 supplies the enable signal ENAB to the second addressmemory controller 16 b. Furthermore, the module controller 12 transmitsa memory control signal AMC, such as a command and an address, to theaddress memory controller 16 on a signal line SIMB.

Referring to FIG. 26, operation of the memory system 10 will now bedescribed. FIG. 26 illustrates signals transmitted and received betweenthe module controller 12 and the second address memory controller 16 bin the eighth embodiment. The module controller 12 starts a read of datafrom the nonvolatile memory 17 at a particular timing. For that purpose,the module controller 12 asserts the signal /CS and ENAB, outputs theread clock CLKB, and transmits a second read command (no address readcommand) to the nonvolatile memory 17 on the signal line SI. The secondread command is different from the regular read command accompanied by aread address, and is illustrated by F3h, for example. The second readcommand instructs using a read address received separately as the startposition to read data consecutively from the start address and thefollowing addresses. The module controller 12 transmits no address valueto the nonvolatile memory 17 after the second read command.

The read address of the start position is generated by the addressmemory controller 16 from the address information in the second addressmemory 15 b. Specifically, when the second address memory controller 16receives an asserted enable signal ENAB, it reads the addressinformation in the second address memory 15 b. As described above, theaddress information in the second address memory 15 b indicates theaddress of the area of the nonvolatile memory 17 from which the data wasread last. When the second address memory controller 16 receives theaddress information in the second address memory 15 b, it increments thereceived address information by a particular amount (for example, 1) togenerate a read address. The second address memory controller 16transmits the generated read address to the nonvolatile memory 17.

When the nonvolatile memory 17 receives the second read command, itrecognizes the second read command and executes the operation instructedby the second read command. Specifically, the nonvolatile memory 17reads data from the read address received from the second address memorycontroller 16 b, and transmits the read data of one byte to the outputcircuit 19. For additional reads, the module controller 12 maintains theasserted enable signal /CS and keeps outputting the read clock CLKB.While the nonvolatile memory 17 keeps receiving the asserted enablesignal /CS and the read clock CLKB, it executes consecutive reads.Specifically, the nonvolatile memory 17 keeps incrementing the readtarget address by a unit amount and reads data from the resultantaddresses. FIG. 26 illustrates a case of a read started from one readaddress, and four bytes read data are output in this way.

When a series of reads is completed, the module controller 12 negatesthe enable signal ENAB as in the write. When the enable signal ENAB isnegated, the second address memory controller 16 b writes the addressinformation in the second address memory 15 b. The address informationwritten in the second address memory 15 here is the last address of aseries of the read accesses, and will be read to be the initial valuewhen the enable signal ENAB is asserted the next time. The modulecontroller 12 then stops the power supply by the power supply circuit11.

Furthermore, the second read command may instruct the output of dataafter a lapse of a particular period, as a variation. FIG. 27illustrates signals transmitted and received between the modulecontroller and the address memory controller in the second example ofthe eighth embodiment. For convenience, the second read command of FIG.27 is referred to as a third read command, and is illustrated by D3h,for example.

The nonvolatile memory 17 may receive a clock of a high frequency. Forexample, the nonvolatile memory 17 receives the read clock CLKB of ahigh frequency from the module controller 12. In such a case, thenonvolatile memory 17 may not be ready for outputting read data rightafter the reception of the read command. In order to address such acase, a read command which instructs data output after a lapse of afixed period after the read command may be defined. Such a read commandis different from the regular read command, and it corresponds to a FASTread command in the SPI. The third read command corresponds to such aread.

When the nonvolatile memory 17 receives the third read command, itrecognizes the third read command and executes the operation instructedby the third read command. Specifically, the nonvolatile memory 17 firstwaits for a particular period. The wait time may be set in advance ordynamically. After the lapse of the wait time (or, dummy cycle) afterthe receipt of the third command, the nonvolatile memory 17 reads datafrom the read address received from the second address memory controller16 b, and transmits the read data to the output circuit 19. FIG. 27illustrates an example of the dummy cycle being eight clocks or equal toa period for transmitting eight bits.

As described, according to the eighth embodiment, the read addressgenerated from the second address memory 15 b is used to execute theread, and therefore the input of the read address accompanying the readcommand is unnecessary. For this reason, reads can be executed withlittle power consumption.

Ninth Embodiment

The ninth embodiment is based on the eighth embodiment. In the ninthembodiment, there is provided a mechanism to update and/or read theaddress information in the second address memory 15 b. The block diagramof the memory system 10 according to the ninth embodiment is the same asthat of the eighth embodiment (FIG. 25).

In the ninth embodiment, the module controller 12 is configured toexecute the operation described in the following.

FIG. 28 illustrates signals transmitted and received between the modulecontroller 12 and the second address memory controller 16 b in the ninthembodiment. The update of the address information in the second addressmemory 15 b may be requested. The update request is made from outsidethe memory system 10 to the module controller 12, for example. Theupdate request is received with new address information.

When address information update is requested, the module controller 12asserts the enable signal ENAB, outputs the write clock CLK, andtransmits a second address write command (read address write command) tothe second address memory controller 16 b on the signal line SIB. Thesecond address write command is different from the regular write commandand the address write command, and is illustrated by FIG. 28 as C2h, andhas a size of one byte, for example. The module controller 12 transmitsthe value of the new address to the second address memory controller 16b on the signal line SIMB after the second address write command. Theaddress has a size of four bytes, for example. When the second addressmemory controller 16 b receives the second address write command, itupdates the value in the second address memory 15 b with the value ofthe address received from the module controller 12. When the update ofaddress information is completed, the module controller 12 negates theenable signal ENA.

Furthermore, the address information in the second address memory 15 bmay be requested from outside the memory system 10. The request of readof address information is made from outside the memory system 10 to themodule controller 12, for example.

In order to deal with such a request, a second address read command canbe defined. FIG. 29 illustrates signals transmitted and received betweenthe module controller 12 and the second address memory controller 16 bin the second example of the ninth embodiment.

When a read of the address information is requested, the modulecontroller 12 asserts the enable signal ENAB, outputs the read clockCLKB, and transmits the second address read command (read address readcommand) to the second address memory controller 16 b on the signal lineSIB. The second address read command is different from the usual readcommand and the address read command, and is illustrated by FIG. 29 asC3h, and has a size of one byte, for example.

When the second address memory controller 16 b receives the secondaddress read command, it recognizes the second address read command,reads the address information in the second address memory 15 b, andtransmits the read address information to the module controller 12 onthe signal line SOMB. FIG. 29 illustrates an example of the addressinformation of four bytes. When the read of address information iscompleted, the module controller 12 negates the enable signal ENA.

As described, according to the ninth embodiment, the address informationin the second address memory 15 b can be written from outside the memorysystem 10 by the second address write command. Moreover, the addressinformation in the second address memory 15 b can be accessed fromoutside the memory system 10 by the second address read command.

Tenth Embodiment

The tenth embodiment relates to an error correction technique.

An error correction technique may be used with a memory device. In thiscase, a circuit to execute an error correction technique, or an errorcorrection circuit, is provided along with a memory device. The errorcorrection circuit receives write data to be written in the memorydevice, follows predefined rules for generating an error correction codeto generate an error correction code (parity), and outputs the set ofwrite data and parity. The memory device stores the set of write dataand parity. Moreover, the error correction circuit receives a set ofread data requested to be read and parity, uses the parity to correct anerror in the read data, and outputs the error-corrected read data.

As an error correction code, a Hamming code is known. The operation forgenerating the Hamming code generates a four-bit parity from eight-bitinformation (substantial data), and, as a result, generates a twelve-bitcode in total, which is a set of information and parity. In other words,the error correction using the Hamming code can correct any one-biterror in an array of twelve bits, but cannot correct errors of two bitsor more.

A BCH code is known as a code which can correct errors of more bits thanwith the Hamming code. The operation for generating the BCH code tocorrect errors of k bits in the information of the length of 2^(m)−1 (mbeing an integer) results in information length=code length−k×m. Forexample, m=4 and k=2 results in the information length of seven bits forthe code length of fifteen bits, and therefore the maximum number ofcorrectable bits with eight-bit parity is seven-bit information. Withm=5 and sixteen-bit code length, the information length is only 16−m×k=6bits.

In contrast, the error correction technique of the tenth embodiment usesa parity generation matrix of FIG. 30. FIG. 30 illustrates an example ofthe parity generation matrix according to the tenth embodiment. Theparity generation matrix has components of eight rows and eight columns.In a parity generation matrix of the tenth embodiment, the set ofcomponents in a particular column has a set of components in an adjacentcolumn with the components cyclically shifted by one row. Specifically,the value at the n^(th) row in the m^(th) column is the same as that atthe (n+1)^(th) row in the (m+1)^(th) column. Moreover, the value at theeighth row in the m^(th) column is the same as that at the first row inthe (m+1)^(th) column, and eight values are cyclically shifted by onerow over the eight columns. Moreover, the value at the n^(th) row in theeighth column is the same as that at the (n+1)^(th) row in the firstcolumn. The value at the eighth row in the eighth column is the same asthat at the first row in the first column.

As illustrated in FIG. 30, the first column has values of 1, 1, 1, 0, 1,0, 0, and 0 at the first to eighth rows, respectively. The second toeighth columns have components determined in accordance the rulesdescribed above.

Referring to an instance of FIG. 31, generation of error correction codeaccording to the tenth embodiment will now be described. FIG. 31illustrates an example of the operation to generate the parity accordingto the tenth embodiment, and illustrates an example of parity generationusing the parity generation matrix of FIG. 30. Data have a size of eightbits and values of D7, D6, D5, D4, D3, D2, D1, and D0 from the mostsignificant bit to the least significant bit, respectively. In order togenerate the parity of this data, data is treated as a matrix of eightrows and one column. Specifically, the data matrix has values of D0, D1,D2, D3, D4, D5, D6, and D7 in the first to eighth rows, respectively.Such a data matrix and the parity generation matrix are multiplied toresult in a parity matrix of eight rows and one column. The paritymatrix has values of P0, P1, P2, P3, P4, P5, P6, and P7 in the first toeighth rows, respectively. Specifically, in the FIG. 31 example, valueP0 is D0+D4+D6+D7, and is the exclusive OR of D0, D4, D6, and D7.Similarly, the other results are P1=D0+D1+D5+D7, P2=D0+D1+D2+D6,P3=D1+D2+D3+D7, P4=D0+D2+D3+D4, P5=D1+D3+D4+D5, P6=D2+D4+D5+D6, andP7=D3+D5+D6+D7. The resultant eight-bit data and the eight-bit parityare concatenated to be treated as an array of sixteen bits in total.

Error correction according to the tenth embodiment will now be describedwith reference to the instances of FIGS. 32 and 33. FIG. 32 illustratesan example of the decryption matrix according to the tenth embodiment,and illustrates the example of the decryption matrix based on the FIG.31 example. FIG. 33 illustrates the operation for the error correctionwith the decryption matrix of FIG. 32. As illustrated in FIG. 32, adecryption matrix of the tenth embodiment has components in eight rowsand sixteen columns. The first to eighth columns of the decryptionmatrix are the same as the first to eighth columns of the paritygeneration matrix of FIG. 30, and the ninth to sixteenth columns of thedecryption matrix are a unit matrix of eight rows and eight columns. Asillustrated in FIG. 33, the decryption matrix of FIG. 32 is multipliedwith the sixteen bits of data and parity obtained by the operation ofFIG. 30. The data and parity are treated in the form of a matrix ofsixteen rows and one column. Specifically, the data and parity bits havevalues D0, D1, D2, D3, D4, D5, D6, D7, P0, P1, P2, P3, P4, P5, P6, andP7 in the first to sixteenth rows, respectively. The multiplicationresults in a syndrome matrix of eight rows and one column. The syndromematrix has values S0, S1, S2, S3, S4, S5, S6, and S7 in the first toeighth rows, respectively.

When there is no error in the sixteen-bit data and parity, the syndromematrix is a zero matrix, i.e., S0=S1=S2=S3=S4=S5=S6=S7=0. In contrast,when data and parity include a one-bit error, the syndrome matrix hasvalue of one at the components at the positions determined in accordancewith the position of the error. Specifically, when value D0 includes theerror, the syndrome matrix is the same as the first column of thedecryption matrix. Similarly, when values D1, D2, D3, D4, D5, D6, D7,P0, P1, P2, P3, P4, P5, P6, and P7 include the error, the syndromematrix is the same as the second to sixteenth columns of the decryptionmatrix, respectively. For example, when value P0 is erroneous, thesyndrome matrix has 1, 0, 0, 0, 0, 0, 0, and 0 in the first to eighthrows, respectively. When value D3 is erroneous, the syndrome matrix has0, 0, 0, 1, 1, 1, 0, and 1 in the first to eighth rows, respectively.

Furthermore, when the data and parity include two-bit errors, theresultant syndrome matrix is an exclusive OR (XOR) of two columns in thedecryption matrix corresponding to the positions of the erroneous bits.For example, when values D0 and D1 are erroneous, the syndrome matrixhas, in the first to eighth rows, respectively, 1, 0, 0, 1, 1, 1, 0, and0, which are XOR of the respective components of the corresponding setof 1, 1, 1, 0, 1, 0, 0, and 0 and the other corresponding set of 0, 1,1, 1, 0, 1, 0, and 0.

In general, the parity generation matrix of the tenth embodimentincludes components such that the XOR of any two of sixteen columns ofthe decryption matrix including that parity generation matrix and a unitmatrix is different from the XOR of any other two columns and any ofsixteen columns of the decryption matrix.

Thus, the error correction technique of the tenth embodiment uses theparity generation matrix, the decryption matrix, and the operation ofFIGS. 30 to 33. As described above, while the Hamming code cannotcorrect two-bit errors in eight-bit data, the error correction techniqueof the tenth embodiment can correct two-bit errors in eight-bit data.The error correction technique with the BCH code can correct two-biterrors in eight-bit data, but the correction in such a case requiresten-bit parity. In contrast, the error correction technique of the tenthembodiment can correct two-bit errors in eight-bit data with eight-bitparity.

The error correction technique of the tenth embodiment can be used witha memory device. Specifically, an error correction circuit of the tenthembodiment receives write data, generates parity from the write data inaccordance with the error correction technique of the tenth embodiment,and outputs the set of the write data and the parity. Moreover, theerror correction circuit of the tenth embodiment receives the set ofread data and parity, uses the error correction technique of the tenthembodiment and the parity to correct an error in the read data, andoutputs the error-corrected read data.

The error correction circuit of the tenth embodiment is applicable tothe first to ninth embodiments, and this will be described withreference to an instance below. In general, error correction circuitsincluding one according to the tenth embodiment may be provided in thechip of a memory device or outside the memory chip. An example where theerror correction circuit is provided in the chip of a memory device inaccordance with the first embodiment (FIG. 17) will be described withreference to FIG. 34. FIG. 34 is a block diagram of the nonvolatilememory 17 according to the tenth embodiment.

The nonvolatile memory 17 includes an error correction circuit 27between the column controller 22 and the input and output circuit 23.The error correction circuit 27 uses the error correction technique ofthe tenth embodiment, i.e., the error correction technique with theparity generation matrix, the decryption matrix, and the operation ofFIGS. 30 to 33, to correct errors in data. Specifically, the errorcorrection circuit 27 receives write data from the input and outputcircuit 23, uses the error correction technique of the tenth embodimentto generate parity from the write data, and outputs the set of writedata and parity to the column controller 22. Moreover, the errorcorrection circuit 27 receives the set of read data and parity from thecolumn controller 22, corrects an error in the read data based on asyndrome obtained through the read data and parity and the errorcorrection technique of the tenth embodiment, and outputserror-corrected read data to the input and output circuit 23.

Although the information length is as short as eight bits in length, theerror correction circuit 27 can correct two-bit errors in data throughaddition of eight-bit parity. The number of bits of parity is fewer thanin the case of the BCH code. For this reason, the error correctioncircuit 27 is useful for an application which treats small data with lowpower, and the first to ninth embodiments correspond to suchapplication.

The parity generation matrix of FIG. 30 is an example, and the paritygeneration matrix of the tenth embodiment is not limited to that of FIG.30. The parity generation matrix can include components different fromthose in the FIG. 30 example as long as the parity generation matrix ofthe tenth embodiment includes components such that the XOR of any two ofsixteen columns of the decryption matrix including that paritygeneration matrix and a unit matrix is different from the XOR of anyother two columns and any of sixteen columns of the decryption matrix.The inventor confirmed existence of at least 5040 parity generationmatrices which fulfill such conditions. FIGS. 35 to 39 illustrateexamples of five parity generation matrices among them. FIGS. 35 to 37,in particular, illustrate examples of a cyclic type, where a set ofcomponents in a particular column is the same as theone-row-cyclically-shifted version of the set of components in anadjacent column. FIG. 38 and FIG. 39 illustrate examples of anon-cyclical type.

As described, the parity generation matrix of the tenth embodimentincludes components such that the XOR of any two of sixteen columns ofthe decryption matrix including that parity generation matrix and a unitmatrix is different from the XOR of any other two columns and any ofsixteen columns of the decryption matrix. The use of such paritygeneration matrix and decryption matrix can correct two-bit errors ineight-bit data. Specifically, the error correction technique of thetenth embodiment exhibits a higher error-correction capability than thecapability of the Hamming code through the use of the parity of bitsfewer than the bits of parity required by the BCH code.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A memory device comprising: memory cells whichstore data in a nonvolatile manner; an error correction circuit which:receives write data, uses the write data and a first matrix to executean operation to generate parity, receives read data and parity based onfrom the read data, uses the read data, the parity based on the readdata and a second matrix to generate a syndrome, uses the syndrome tocorrect an error of the read data, wherein the second matrix includesthe first matrix and a unit matrix, and the first matrix comprisescomponents selected such that an XOR of any two columns of the secondmatrix is different from an XOR of any other two columns and any columnof the second matrix; and a controller which writes the write data andthe parity based on the write data in memory cells, and supplies theread data and the parity based on the read data from memory cells to theerror corrections circuit.
 2. The device of claim 1, wherein: the firstmatrix comprises components in eight rows and eight columns, and thesecond matrix comprises components in eight rows and sixteen columns. 3.The device of claim 2, wherein: the write data comprises components ineight rows and one column, and the error correction circuit multipliesthe first matrix and the write data to generate parity of eight rows andone column.
 4. The device of claim 2, wherein: the second matrixcomprises the first matrix in first to eighth columns and a unit matrixin ninth to sixteenth columns, the read data comprises components ineight rows and one column, the error correction circuit multiplies thesecond matrix and an input which comprises the read data in first toeighth columns and the parity based on the read data in ninth tosixteenth columns to generate the syndrome, and the syndrome comprisescomponents in eight rows and one column.
 5. The device of claim 4,wherein: the first matrix comprises only components of one or zero, andwhen the input has an error in a k^(th) column (k being a natural numbernot greater than sixteen), the syndrome is the same as a k^(th) columnof the second matrix.
 6. The device of claim 5, wherein: when the inputhas errors in a k^(th) column and h^(th) column (h being a naturalnumber different from k and not greater than sixteen), the syndrome isthe same as an XOR of a k^(th) column and an h^(th) column of the secondmatrix.
 7. The device of claim 2, wherein: the first matrix comprises:in an n^(th) row in an m^(th) column, the same component as a componentin an (n+1)^(th) row in an (m+1)^(th) column; and in an eighth row inthe m^(th) column, the same component as a component in a first row inan (m+1)^(th) column, where each of m and n is a natural number notgreater than seven.